Drive controller for a self-commutated converter

ABSTRACT

A drive controller for a self-commutated converter having two half-bridges with converter valves, includes two control circuits, with each control circuit associated with a corresponding half-bridge and operatively connected with the converter valves of that half-bridge, and at least two switches, wherein an input of each switch is directly or indirectly connected to an external voltage, and an output of each switch is directly or indirectly connected to a pulse-inhibiting path. Further provided are at least two pulse-inhibiting controllers, wherein each switch receives control signals from a corresponding one of the pulse-inhibiting controllers. Arranged in the pulse-inhibiting path is a buffer unit for briefly maintaining a supply voltage of the control circuits if a pulse-inhibiting path electrically disconnects at least one of the control circuits from the external voltage. Thus, the drive controller, and more particularly its pulse-inhibiting paths, can be tested cyclically without interrupting the operation of the drive controller.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application,Serial No. 103 07 997.1, filed Feb. 25, 2003, pursuant to 35 U.S.C.119(a)-(d), the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a drive controller for aself-commutated converter, and more particularly to a drive controllerwith pulse-inhibiting paths that can be cyclically tested withoutservice interruption.

Great care must be exercised when using electric drives in industrialautomation applications, for example with numerically controlledmachine-tools and robots, to protect men and machine as safely aspossible. The electrical machine or the motor should be prevented fromperforming dangerous movements even when a single error occurs, byimplementing a “safe stop” function for the motor. This function istypically initiated depending on the operating mode, e.g., before aprotective door is opened.

The “safe stop” function is implemented by disconnecting the electricpower at two places, for example, by also disconnecting the motor. It isgenerally accepted to separately disconnect the lower and/or upperconverter valves of a self-commutated converter employing a bridgecircuit.

A “safe stop” function can be implemented by “safely” inhibiting thecontrol signals to the converter valves, referred to in the art also as“pulse inhibit”, or to disconnect all converter valves. The term“safely” is intended to indicate that the regulatory requirementsimposed or suggested by the professional organizations or regulatorybodies for occupational safety are satisfied.

A drive controller of this type is known from the German patent no. DE100 59 173. This conventional drive controller is shown in detail inFIG. 1. The self-commutated converter W has two half-bridges withconverter valves T1, T3, T5, and T2, T4, T6, respectively. The drivecontroller has a separate control circuit for each half-bridge. Of thecontrol circuits, only the associated opto-couplers OK1, OK3, OK5 forthe upper half-bridge, and OK2, OK4, OK6 for the lower half-bridge areshown in FIG. 1. The anodes of the photodiodes of the opto-couplers OK1,OK3, OK5 and OK2, OK4, OK6 are electrically connected with respectivesupply voltages SV1 and SV2, whereas the cathodes are electricallyconnected with corresponding pulse-inhibiting circuits I1 and I2 viaresistors RS1, RS3, RS5, and RS2, RS4, RS6, and forward-biased diodesDS1, DS3, DS5, and DS2, DS4, DS6 connected downstream of the resistors.The respective supply voltages SV1 and SV2 are present at correspondingoutputs of pulse-inhibiting paths IP1 and IP2. Each of thepulse-inhibiting paths IP1 and IP2 is connected to the supply voltage SVvia a corresponding switch S1 and S2, whereby the switches S1 and S2receive control signals from associated pulse-inhibiting circuits I1 andI2. The output side of each pulse-inhibiting path IP1 and IP2 isconnected to an associated pulse-inhibiting circuit I1, I2 via adiagnostic line which includes a decoupling diode, supplyingcorresponding diagnostic signals SV1_Diag and SV2_Diag to thepulse-inhibiting circuits I1 and I2.

The function “safe stop” is implemented by a pulse-inhibiting circuitwhich is used to switch the converter valves T1 to T6 of the inverter Woff during normal operation or when a fault is detected. Preferably, thesupply voltage SV1 for the opto-couplers OK1, OK3, OK5 for the upperbridge arm, which is derived from an external voltage SV, is interruptedby switch S1 (either a mechanical or an electronic switch) by applying asignal IL1 from the pulse-inhibiting circuit I1. Another supply voltageSV2 for the opto-couplers OK2, OK4, OK6 for the lower bridge arm isinterrupted by switch S2 (either a mechanical or an electronic switch)by applying a signal IL2 from the pulse-inhibiting circuit I2, as wellas by inhibiting the pulses in the control set ST.

The operation of the two pulse-inhibiting paths IP1 and IP2 with theswitches S1 and S2 can be tested cyclically, for example each time afterthe supply voltage is switched on. For this purpose, the pulsecontroller I1 reads the supply voltage SV1 through the signal SV1_Diag,whereas the pulse controller I2 reads the supply voltage SV2 through thesignal SV2_Diag, which are provided after the switches S1 and S2,respectively. Even if one of the pulse controllers I1 and I2 fails, theother properly operating pulse-inhibiting controller I2 or I1 can stillrespond, since the aforedescribed cyclically performed tests can detecteven so-called dormant errors.

Disconnectable paths have to be tested for errors, since the probabilityof a component failure is never zero. As mentioned above, the function“safe stop” requires two redundant disconnectable paths which arechecked at predefined test intervals, for example every eight hours.This guarantees the required protection against single faults. However,the operation of the device needs to be interrupted for the test, whichmakes more frequent tests of the disconnectable paths impractical.

It would therefore be desirable and advantageous to improve thedisconnectable voltage supplies of conventional drive controllers byobviating prior art shortcomings, so that the disconnectable paths ofdrive controllers can be tested without service interruption.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a drive controller for aself-commutated converter having two half-bridges with converter valvesis disclosed. The drive controller includes two control circuits,wherein each control circuit is associated with a correspondinghalf-bridge and operatively connected with the converter valves of thathalf-bridge. The drive controller further includes at least twoswitches, wherein an input of each switch is directly or indirectlyconnected to an external voltage and an output of each switch isdirectly or indirectly connected to a pulse-inhibiting path. The drivecontroller also includes at least two pulse-inhibiting controllers,wherein each switch receives control signals from a corresponding one ofthe pulse-inhibiting controllers, and a buffer unit arranged in thepulse-inhibiting path for briefly maintaining a supply voltage of thecontrol circuits if a pulse-inhibiting path electrically disconnects atleast one of the control circuits from the external voltage.

By connecting each pulse-inhibiting path downstream of the switch andbriefly maintaining the supply voltage of the control circuit, thepulse-inhibiting paths can be tested at any time without serviceinterruption. The buffer unit for maintaining a supply voltage isdimensioned so that the supply voltage does not noticeably decreaseduring the test interval. Since testing is done without serviceinterruption, this test can be conducted at any time.

Embodiments of the invention may include one or more the followingfeatures. The buffer unit can include a support capacitor having oneinput connected to ground and another input connected to a decouplingdiode. The capacitance value of the support capacitor can be selected soas to maintain the supply voltage during the test. Alternatively, thebuffer unit can include a support capacitor having one input connectedto ground and another input connected to an output of a storageinductance, and a free-wheeling diode connected between an input of thestorage inductance and ground.

Moreover, a load resistor can be electrically connected in parallel withthe support capacitor. This load resistor renders the device independentof the load current through the opto-couplers of the two controlcircuits of the drive controller. In addition, the load resistorprovides for a quick discharge of the support capacitor when the drivecontroller is turned off for longer periods of time.

To facilitate testing, the buffer unit can have an input operating as adiagnostic terminal. In addition, a short-circuit in thepulse-inhibiting path can also be identified during the cyclicallyperformed tests without service interruption.

In a conventional drive controller with two pulse-inhibiting paths, twodevices for briefly maintaining a supply voltage can be employed.However, if a drive controller has only one pulse-inhibiting path, thentwo switches in this path can be connected in series. Since only onepulse-inhibiting path is provided, only one device for brieflymaintaining the supply voltage is required.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be morereadily apparent upon reading the following description of currentlypreferred exemplified embodiments of the invention with reference to theaccompanying drawing, in which:

FIG. 1 is a block diagram of a conventional drive controller having thefunction “safe stop”;

FIG. 2 is a block diagram of a first embodiment of a device for apulse-inhibiting path in accordance with the present invention;

FIG. 3 is a block diagram of a second embodiment of a device for apulse-inhibiting path in accordance with the present invention; and

FIG. 4 is a block diagram of a modification of the device for apulse-inhibiting path of FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the Figures, same or corresponding elements are generallyindicated by same reference numerals. These depicted embodiments are tobe understood as illustrative of the invention and not as limiting inany way. It should also be understood that the drawings are notnecessarily to scale and that the embodiments are sometimes illustratedby graphic symbols, phantom lines, diagrammatic representations andfragmentary views. In certain instances, details which are not necessaryfor an understanding of the present invention or which render otherdetails difficult to perceive may have been omitted.

Turning now to the drawing, and in particular to FIG. 2, there is shownin greater detail a first embodiment of a drive controller A′ inaccordance with the invention. For the sake of simplicity, FIGS. 2 to 4depict only those parts that are necessary for the understanding of thepresent invention, so that the self-commutated converter W and themotor, as shown in FIG. 1, are not shown here.

The drive controller A′ is different from the conventional drivecontroller A of FIG. 1 in that a unit VA for briefly maintaining asupply voltage SV12 of two control circuits is arranged in thepulse-inhibiting path IP. In contrast to the embodiment of FIG. 1, thedrive controller A′ has only one pulse-inhibiting path IP, in which thetwo switches S1 and S2, which are electrically connected in series, areinserted. Each switch S1 and S2 is opened by a control signal IL1 andIL2 received from two pulse-inhibiting controllers I1 and I2. Thepulse-inhibiting controllers I1 and I2 are not shown in detail. A supplyvoltage SV12 derived from an external voltage SV is present at theoutput of switch S2. This voltage SV12 is buffered by the unit VA whichis connected after the pulse-inhibiting path IP for briefly maintainingthe supply voltage. The buffered supply voltage SV12′ represents thesupply voltage of the two control circuits for the converter valves T1to T6 of the self-commutated converter W.

The block diagram of the unit VA depicted in FIG. 2 represents apreferred embodiment. The unit VA includes a support capacitor C whichis connected to ground. This support capacitor C is decoupled via adecoupling diode D from the series-connected switches S1 and S2, so thatthe support capacitor cannot be discharged in the normal operatingstate, i.e., when the pulses are enabled. This circuit also includes aload resistor R which is connected electrically in parallel with thecapacitor C. This load resistor R renders the unit VA, which is intendedto briefly maintaining the buffered supply voltage SV12′, independent ofthe load current through the opto-couplers OK1 to OK6. Moreover, thesupport capacitor C can be immediately discharged during a stationaryturn-off.

In the normal operating state of the pulse-inhibiting path IP, the twoswitches S1 and S2 are closed. The support capacitor C is then charged,and a buffered supply voltage VA12′ is supplied at the output of theunit VA. The capacitance value of the support capacitor C is selected sothat during the cyclically performed tests, which are conducted withoutservice interruption, the supply voltage SV12′ does not decreasesignificantly. Depending on the control signals IL1 and IL2 of thepulse-inhibiting controller I1 and I2, the switch S1 and S2 can bebriefly opened. After one of the two switches S1 and S2 is opened, thefunctionality of the opened switch S1 or S2 is tested by measuring thediagnostic signal SV12_Diag at the input of the unit VA. If thisdiagnostic signal SV12_Diag is zero after a switch S1 or S2 has beenopened, then the opened switch S1 or S2 is functional. The same test isperformed on the second switch S2 or S1.

FIG. 3 depicts a second embodiment of the unit VA for thepulse-inhibiting path IP. This embodiment is different from theembodiment of FIG. 2 in that a storage inductance L is provided insteadof the decoupling diode D. At the input, a free-wheeling diode DF isconnected to ground. In this embodiment, too, a load resistor R isconnected parallel with the support capacitor C. Accordingly, the secondembodiment of the unit VA can also be regarded as an advantageousembodiment.

In the normal operating state (pulses enabled), the two switches S1 andS2 are closed. The support capacitor C is charged, so that a bufferedsupply voltage SV12′ of a predetermined magnitude is present at theoutput of the unit VA. Depending on the pulse-inhibiting controller I1and the I2, a switch S1 or S2 is opened. As a result of the opening ofone of the two switches S1 and S2 of the pulse-inhibiting path IP, thecurrent commutates through the storage inductance L to the free-wheelingdiode DF. As a result, the value of the input voltage U1 decreases to anegative forward diode voltage. This value is supplied to thecorresponding pulse-inhibiting controller I1 or I2 by the diagnosticsignal SV12_Diag. If the input voltage U1 decreases every time to thepredetermined value, then the switches S1 and S2 are functional. If thevalue of the input voltage U1 of the unit VA remains at the value of theexternal voltage SV, then the tested switch S1 or S2 has ashort-circuit. The switches S1 and S2 are tested without serviceinterruption.

FIG. 4 shows in greater detail a block diagram of a modification of thedrive controller of FIG. 3. Unlike the embodiment of FIG. 3, the drivecontroller includes two pulse-inhibiting paths IP1 and IP2. A unit VAfor briefly maintaining the supply voltage SV1 and SV2 is arranged ineach pulse-inhibiting path IP1 and IP2. The unit VA corresponds to theunit VA of FIG. 3. By using two pulse-inhibiting paths IP1 and IP2, thepulses can be blocked either for the converter valves T1, T3, T5, or forthe converter valves T2, T4, T6, or also for all converter valves T1 toT6 of the self-commutated converter W. In all other aspects, thecyclical tests are performed in the same manner as in the embodiment ofFIG. 3, again without service interruption.

By using a storage inductance L in the embodiment of FIGS. 3 and 4, ashort-circuit between the external voltage SV and the buffered supplyvoltage SV12′ and/or the buffered supply voltage SV1′ and/or SV2′ can bedetected without requiring or causing a service interruption. If ashort-circuit KS occurs in the pulse-inhibiting path, as described withreference to the exemplary embodiment of FIG. 3, then no current flowsthrough the storage inductance L. After the switches S1 and S2 areopened, the current is not commutated, so that the value of the voltageSV12 remains the same as the external voltage SV.

While the invention has been illustrated and described in connectionwith currently preferred embodiments shown and described in detail, itis not intended to be limited to the details shown since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention. The embodiments werechosen and described in order to best explain the principles of theinvention and practical application to thereby enable a person skilledin the art to best utilize the invention and various embodiments withvarious modifications as are suited to the particular use contemplated.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims and includes equivalents of theelements recited therein:

1. A drive controller for a self-commutated converter having twohalf-bridges with converter valves, said drive controller comprising:two control circuits, each control circuit being associated with acorresponding half-bridge and operatively connected with the convertervalves of that half-bridge; at least two switches, each switch having aninput that is directly or indirectly connected to an external voltageand an output that is directly or indirectly connected to apulse-inhibiting path; at least two pulse-inhibiting controllers, eachswitch receiving control signals from a corresponding one of thepulse-inhibiting controllers; and a buffer unit arranged in thepulse-inhibiting path for briefly maintaining a supply voltage of thecontrol circuits if a pulse-inhibiting path electrically disconnects atleast one of the control circuits from the external voltage.
 2. Thedrive controller of claim 1, wherein the buffer unit includes a supportcapacitor having one input connected to ground and another inputconnected to a decoupling diode.
 3. The drive controller of claim 1,wherein the buffer unit includes a support capacitor having one inputconnected to ground and another input connected to an output of astorage inductance, and a free-wheeling diode connected between an inputof the storage inductance and ground.
 4. The drive controller of claim2, wherein a load resistor is connected electrically in parallel withthe support capacitor.
 5. The drive controller of claim 3, wherein aload resistor is connected electrically in parallel with the supportcapacitor.
 6. The drive controller of claim 1, wherein the buffer unithas an input operating as a diagnostic terminal.
 7. The drive controllerof claim 1, wherein the at least two switches are electrically connectedin series, with a first of the at least two switches being directlyconnected to the external voltage and a second of the at least twoswitches being directly connected to the pulse-inhibiting path.
 8. Thedrive controller of claim 1, wherein the inputs of the at least twoswitches are directly connected to an external voltage and the output ofeach switch is directly connected to a different pulse-inhibiting path,with the different pulse-inhibiting paths disconnecting differentcontrol circuits.